1. Field of the Invention
The present invention relates to an encoding apparatus and method, a decoding apparatus and method, and distribution media, and more particularly to an encoding apparatus and method, a decoding apparatus and method, and distribution media for performing encoding and decoding by use of a finite-state transition diagram.
2. Description of the Related Art
A block encoding method is well-known as a conventional recording/encoding method. That is, this method performs block conversion from m-bit data into n-bit code words. In this case, the size of blocks for block conversion has a close relation to the ease of manufacturing an apparatus. An encoding rate is represented by m/n; two encoding rates m/n=8/10 and m/n=10/20 will be considered herein. Although both are the same in encoding rate, the block size in the latter is twice as large.
In the encoding of m/n=8/10, 2.sup.8 code words are selected from 2.sup.10 code words. In the encoding of m/n=16/20, 2.sup.16 code words are selected from 2.sup.20 code words. In this case, apparently, the latter has more code word candidates and greater freedom. Accordingly, when required restrictions are imposed on codes, more strict conditions can be put on the latter codes. This suggests the possibility that more efficient codes can be generated.
However, the following drawback exists in the above-described block conversion technique. As in an encoder shown in FIG. 16A and a decoder shown in FIG. 16B, when they are configured with ROM (Random Access Memory), PLA (Programmed Logic Array), or random logic circuits, the circuit size becomes larger like an exponential function for codes of large blocks, e.g., m/n=16/20, than for codes of small blocks, e.g., m/n=8/10. In other words, for codes of m/n=8/10, a table showing a one-to-one correspondence between 2.sup.8 pieces of data and code words are embodied with an encoder and a decoder, while, for codes of m/n=16/20, a table showing a one-to-one correspondence between 2.sup.16 pieces of data and code words must be embodied with an encoder and a decoder.
When an encoder and a decoder are configured with a PLA and a random logic circuit, the way of associating data words with code words exerts a great influence on the apparatus size. For codes of small blocks, it is relatively easy to establish a correspondence suitable for apparatus manufacturing, but the larger the block, the more difficult it becomes to find out a correspondence suitable for apparatus manufacturing.
In the logic synthesis by a logic synthesis program, as a block became larger, processing necessary for the synthesis increases like an exponential function and the processing capacity is exceeded, sometimes resulting in failure of the synthesis and requiring a huge amount of time for the synthesis.